+1 that's a good potion idea.
It would be more fair if there would be a cooldown depending on the time that the used potion lasts. Is half of the time the potion lasted too much?
EDIT: And if you would want to use more than one potion at the same time it would cost 5-10 orbs and the price of the potion. Of course the max potions you could have at the same time would be 3.
Also, what about a double skull gold bonus potion, to get more money? Price could be about 9 orbs, it would last for 12h and cooldown could be 6-8h.
I like the balance of the potion's cool-down is half the duration. So a 6 hour potion has a 3 hour cool-down and 12 hour is 6 and so on. I feel that is fair.
With that balance I'd say it wouldn't be bad to be able to stock them. You could find them in doors and have a supply.